Solvent extraction is a process that separates hydrocarbon mixtures into two phases, a raffinate phase which contains substances of relatively high hydrogen to carbon ratio often called paraffinic type materials and an extract phase which contains substances of relatively low hydrogen to carbon ratio often called aromatic type materials. Therefore, it may be said that solvent extraction is possible because different liquid compounds have different solution affinities for each other and some combinations are completely miscible while other combinations are almost immiscible. The ability to distinguish between high carbon to hydrogen aromatic type and low carbon to hydrogen paraffinic type materials is termed selectivity. The more fine the distinguishment is done, the higher is the selectivity of the solvent.
Solvent extraction of hydrocarbon oils using polar solvents to remove aromatic constituents has long been a standard processing procedure in the Oil Industry. The use of furfural to selectively extract aromatic components from hydrocarbon oils is the subject of many patent, for instance, U.S. Pat. No. 2,079,885, U.S. Pat. No. 2,698,276, U.S. Pat. No. 3,567,627 and U.S. Pat. No. 4,571,295, which are incorporated by reference. In U.S. Pat. No. 5,922,193, ethers or aldehydes is added to furfural to improve the solvent capacity for debottlenecking the extraction unit and claimed 2-3 vol % increase in the raffinate yield during the process. In the prior art, U.S. Pat. No. 4,273,645 additives such as, sodium dodecylbenzene sulfonate or high molecular weight polyethylene oxide resin is added to improve the selectivity of furfural and claimed less than 3 vol % increase in the raffinate yield at solvent dosage of 250 vol %. Further, in the said prior art, the recovery and material balance of the additive employed is not disclosed.